FIG. 12 schematically illustrates an example of a conventional axial-flow type gas laser oscillator. Referring to FIG. 12, a description is provided hereinafter of the conventional axial-flow type gas laser oscillator.
In FIG. 12, discharge tubes 101 are formed of a dielectric such as glass. Electrodes 102, 103 are provided on the periphery of discharge tube 101 and connected to power source 104. Discharge space 105 is located between electrodes 102, 103 inside discharge tube 101. Totally reflecting mirror 106 and partially reflecting mirror 107 are fixedly disposed at respective ends of discharge spaces 105 and form an optical resonator.
Laser beam 108 is output from partially reflecting mirror 107. Laser gas circulates through laser gas passage 110 of the axial-flow type gas laser oscillator and flows in direction 109. Heat exchangers 111, 112 function to lower the temperature of the laser gas that is raised by discharge in discharge space 105 and operation of blower 113. Blower 113 circulates the laser gas and produces a gas flow of about 100 m/sec in discharge space 105. Laser gas passage 110 and discharge tube 101 are connected by laser gas inlet section 114.
A description is provided next of operation of the conventional gas laser oscillator having the above structure.
The laser gas blown by blower 113 passes through laser gas passage 110 and is introduced into discharge tube 101 from laser gas inlet section 114. With the laser gas introduced into discharge tube 101, the discharge is caused in discharge space 105 by electrodes 102, 103 connected to power source 104. In discharge space 105, the laser gas is excited by obtaining this discharge energy. The optical resonator formed of totally reflecting mirror 106 and partially reflecting mirror 107 causes the excited laser gas to be in a resonant condition, and laser beam 108 is output from partially reflecting mirror 107. This laser beam 108 is used for laser beam machining or the like.
There is a conventional structure including a chamber that is provided at some position of the laser gas passage for storing the gas temporarily. This structure suppresses and uniformizes pulsation of the gas by storing the laser gas temporarily in the chamber. Such a structure is disclosed, for example, in Japanese Laid-Open Patent No. H07-142787.
Another attempt is made to damp the pulsation by providing, at some position of the laser gas passage, a resonance chamber set to include a resonance frequency of a compression wave of the laser gas and absorbing vibrational energy of the compression wave by means of a sound absorbing porous material affixed to an inner surface of the container. This structure is disclosed, for example, in Japanese Patent Unexamined Publication No. H02-285686.
The above-described conventional axial-flow type gas laser oscillator, however, has the following problem.
It is desirable that the laser gas should flow stably in discharge tube 101 of the axial gas laser. The stable gas flow stabilizes the condition of the discharge, whereby laser output can be taken efficiently with respect to electrical input to discharge tube 101. If the laser gas flow has the pulsation, such as a pressure change of about tens to hundreds of hertz over time, the condition of the discharge becomes unstable. Consequently, the laser output is reduced.
The axial-flow type gas laser oscillator structurally requires blower 113. An impeller of blower 113 is rotated generally at hundreds of hertz to blow the laser gas. For this reason, the gas flow problematically has the pulsation or the compression wave that synchronizes with the impeller's rotation at hundreds of hertz.
To address this problem, the above-mentioned structure has the chamber that is provided at some position of the laser gas passage for storing the gas temporarily. This structure attempts to suppress and uniformize the pulsation of the gas by storing the laser gas temporarily in the chamber. Although this structure can reduce the pulsation to some extent, the structure is not sufficiently effective in improving the decline in laser output.
The attempt, which is made to damp the pulsation by providing, at some position of the laser gas passage, the resonance chamber set to include the resonance frequency of the compression wave of the laser gas and absorbing the vibrational energy of the compression wave by means of the sound absorbing porous material affixed to the inner surface of the container, is also not sufficiently effective in improving the decline in laser output.